An element formed of a wide band gap semiconductor, representative examples of which include GaN and SiC, has excellent characteristics such as high-speed switching and a low on-resistance value, as compared to an element formed of a silicon semiconductor. Among elements formed of a wide band gap semiconductor, there is an element that exhibits a normally-on property in which a drain current flows even when a gate voltage is 0 V, or an element that exhibits a normally-off property having a low threshold voltage of approximately 2 V. In order to reliably control an element having a normally-on property, the gate voltage needs to be driven to a negative voltage.
PTL 1 discloses a power conversion circuit in which a bridge circuit constituted by upper and lower arms is formed by using normally-on transistors. PTL 2 discloses a protection circuit for an arm short in a driver circuit (inverter circuit) that uses a normally-on transistor. PTL 3 discloses a technique for achieving self-feeding of a power source in a control circuit (driving circuit) of a normally-on transistor.